Japan Priority Application 2000-291890, filed Sep. 26, 2000 including the specification, drawings, claims and abstract, is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to an electromagnetic relay comprising a case with an opening at one end thereof, which covers the whole relay, a spool with a coil as an electromagnet wound therearound, a fixed contact, and a movable contact, wherein a first flange of the spool is located on the opening of the case, a second flange of the spool is located on an inner side of the case, the fixed contact and the movable contact are oppositely disposed at positions closer to the inner part than the second flange of the spool, and a fixed terminal with the fixed contact provided thereon is mounted on the spool.
2. Description of the Related Art
Generally, an electromagnetic relay is constructed such that a movable contact and a fixed contact are located on an opposite side (case inner side) of a terminal side from which connection terminal ends of terminals are derived. The movable contact is moved in an axial direction of the coil to cause a switchover of a conduction state (contact state) to the fixed contact. In such an electromagnetic relay, as described also in Japanese Patent Unexamined Publication No. Sho. 56-93234, it is a common practice that the fixed terminal with the fixed contact secured at one end thereof is secured, by press-fitting or the like, to a thick part of the case-inner-side flange of the resin spool on which a coil is to be wound. Another type of electromagnetic relay is also known. In the electromagnetic relay, the other end (connection terminal end) of the fixed terminal is press fit to a base located outside the terminal-side flange of the spool, whereby the fixed terminal is firmly supported (see FIG. 2 of Japanese Utility Model Unexamined Publication No. Hei. 3-12198).
Size and cost reduction is a strong demand in the small electromagnetic relay (height: 20 mm or less), which is mounted on a printed circuit board used in a motor vehicle. To meet the demand, further reduction of the number of required component parts and further increase of parts assembling density are essential.
An electromagnetic relay presenting a solution to such a problem is disclosed in Japanese Patent Unexamined Publication No. Hei. 10-162712. In the publication, a member called a base, which is conventionally used as the base in assembling the relay parts, is omitted. One of the flanges of the spool, on which a coil for the electromagnet is to be wound, is located inside the opening of the case, and this flange is used for the base.
In this type of small electromagnetic relay, a sealed electromagnetic relay (i.e., sealing type relay) is dominantly used in order to endure the washing process carried out after it is mounted on the printed circuit board, and to secure given water- and dust-proof performance. The washing process is carried out after the soldering for mounting the relay on the printed circuit board. Accordingly, the relay being heated is rapidly cooled by the washing liquid. This gives rise to a pressure difference between the inside and the outside of the relay. In this condition, washing liquid is easily pulled into the relay assembly through gap or gaps even if gap or gaps are small. To avoid this, a high degree of hermeticity is required for the relay assembly.
FIG. 8A shows a diagram of a conventional electromagnetic relay of such a type for the purpose of comparison.
In this relay designated by reference numeral 1, a flange 2a located on the case opened side of a spool 2 is used as a base in assembling the electromagnetic relay. The relay 1 is constructed with the spool 2, an iron core (not shown) of the electromagnet mounted while being inserted into the spool 2, an L-shaped yoke 4, a movable iron member 5, an L-shaped movable contact spring (movable contact terminal) 6, a movable contact 7, a first fixed contact (NC contact) 8, a first fixed terminal 9, a second fixed contact (NO contact) 10, a second fixed terminal 11, first and second coil terminals 12 and 13, and a case 14. A coil 1a forming an electromagnet is wound around the spool 2. The yoke 4 is coupled to the iron core, and provides a magnetic path allowing lines of magnetic force to pass therethrough. The movable iron member 5 is joined at the base end to the top end (=the upper end in FIGS. 8A and 8B) of the yoke 4, and the top end of the movable iron member 5 may be swung under attraction by the iron core when current is fed to the coil. The movable contact spring 6 consists of a plate spring the top end of which may be swung, and mounted on the movable iron member 5 at the top end thereof. The movable contact 7 is mounted to the top end of the movable contact spring 6. The movable contact 7 is in pressing contact with the first fixed contact 8 when no current is fed to the coil. The first fixed contact 8 is mounted on the upper end of the first fixed terminal 9. The movable contact 7 is in pressing contact with the second fixed contact 10 when current is fed to the coil. The second fixed contact 10 is mounted on the upper end of the second fixed terminal 11. The first and second coil terminals 12 and 13 are connected to lead wires of the coil, respectively. An assembling side (=lower side in FIGS. 8A and 8B) of the case 14 is opened.
The strip-like parts of the movable contact spring 6, first fixed terminal 9 and second fixed terminal 11, which are extended to the opened side (=lower end side in FIGS. 8A and 8B) of the case 14, are protruded to positions outside the flange 2a (base) to form connection terminals 21 to 23 used for connecting the individual contacts to given circuit conductors, respectively, like the first and second coil terminals 12 and 13. In FIGS. 8A and 8B, the second coil terminal 13 is located on the opposite side of the first coil terminal 12. The lower end of the first fixed terminal 9 (=connection terminal 22) is also located on the opposite side of the lower end of the second fixed terminal 11 (=connection terminal 23).
In assembling the relay 1, components parts other than the case 14 are assembled, while using the flange 2a as the base member, into a sub-assembly. The case 14 is applied to the sub-assembly to cover the latter. Thereafter, the opening side of the case 14 is sealed with a sealing material 20, e.g., thermosetting resin, to complete an electromagnetic relay.
The first fixed terminal 9 and the second fixed terminal 11 are press-fit to the flange 2a (case-opened-side flange) of the spool 2 at positions indicated as A in FIG. 8A. Those fixed terminals are also press-fit to a flange 2b (case-inner-side flange) of the spool 2 at positions denoted as B in FIG. 8A.
In the relay of the above-mentioned type, there are the following problems.
(1) As described above, the fixed terminals with the fixed contacts secured thereto are secured to the case-inner-side flange, or to both the case-inner-side flange and the case-opening-side flange as shown in FIG. 8A. Therefore, there is a chance that in an abnormal state of overcurrent feeding, the second fixed contact (NO contact) 10 is left in contact with the movable contact 7 (their conduction state is retained).
The reason for this is that in a state where overcurrent is fed to the coil, the coil 1a is heated to high temperature, and hence it is thermally expanded in the axial direction of the coil. As a result, the spool 2 is deformed such that the flanges 2a and 2b are spaced apart from each other as indicated by arrows in FIG. 8A. With the deformation, a part of the second fixed terminal 11 near its position at which the fixed terminal is secured to the flange 2b located at the inner side of the case (i.e., part to which the second fixed contact 10 is secured) moves to the inner side of the case.
Usually, the second fixed contact (NO contact) 10 is connected to a power line of a load (e.g., a motor) for the purpose of power supplying. The first fixed contact (NC contact) 8 is connected to a ground line. Accordingly, if the on state of the NO-contact (conduction holding state) is continued, a fire by the heating thereat may be caused. If the conduction holding state further continues and the above deformation further progresses, the movable contact 7, the first fixed contact (NC contact) 8 and the second fixed contact (NO contact) 10 are brought into contact with one another in a superimposing fashion, as shown in FIG. 8B. In this state, there is a danger that a short circuit occurs between the power source and ground.
(2) Since a part of the fixed terminal near the fixed contact thereof is secured to the case-inner-side flange 2b, a deformation (warp) of the flange 2b in the axial direction of the coil results in a displacement of the fixed contact position (particularly in the coil axial direction). As a result, a pressure of the contact varies, and its characteristic tends to excessively vary. Usually, the coil is densely wound around the spool of the electromagnetic relay and hence, the coil will constantly expand outside. Accordingly, an outside expanding force of the coil (=pressure acting in the coil axial direction) constantly acts on the spool. Because particularly, in the case of the small electromagnetic relay as mentioned above, the flanges of the spool is thin, the flanges of the spool are considerably deformed (warped) by the coil axial direction pressure, as shown in FIG. 9A. As the result of the deformation, the fixed contact also displaces, and its characteristic value will be greatly different from its design value.
Particularly, when thermosetting resin is used for the sealing material, a residual stress within the coil is relatively greatly lessened by the aging after the coil is wound, and the thermosetting process (heating process) of the sealing material after the assembling of the relay (after the sealing material is applied). The inventors of the present patent application discovered the fact: The flanges of the spool, which have expanded outside as shown FIG. 9A, have such a nature that those flanges inwardly displace (mutually approach) to resume their original shape as shown in FIG. 9B.
An effect of a lateral displacement of the contact position of the contact on its characteristic, e.g., contact resistance, is relatively small. In the contact of some size, it will be absorbed to be negligible. On the other hand, a displacement of the fixed contact in a contact direction where the movable contact moves (viz., the coil axial direction) greatly affects the contact pressure, causing a great variation of the characteristic. Particularly, when the thermosetting resin is used for the sealing material, due to the recovery of the spool from its deformation, the case-inner-side flange 2b and the second fixed contact 10 are displaced, by a noticeable extent, toward the opened side of the case (to such a direction in which those move apart from the movable contact 7), after the assembling of the relay. Accordingly, the contact pressure, which was adjusted to have an optimum value (at the time of assembling the component parts within the case), varies to diminish, thereafter. As a result, it is impossible to secure a required contact pressure. The number of the resultant products, which fail to satisfy the required product specifications, is increased (viz., the product yielding reduces). This fact was confirmed by the inventors.
Accordingly, a first object of the present invention is to provide an electromagnetic relay in which flanges of a spool are respectively located at an opened side of the case and an inner part of the case, and a fixed terminal is mounted on the spool, the relay being improved such that even if the coil is thermally expanded, there is no (or little) chance that the NO contact is put in the conduction holding state.
A second object of the present invention is to provide an electromagnetic relay which is free from the decrease of a contact pressure of the NO contact, which results from the recovery of the spool from its deformation in the case of using the thermosetting resin for the sealing material.
According to a first aspect of the invention, there is provided a first electromagnetic relay comprising:
a case having an opening at one end thereof and covering the whole electromagnetic relay;
a spool with a coil as an electromagnet wound therearound, the spool including a first flange disposed inside the case and at an opened side of the case, and a second flange disposed at an inner part of the case;
a fixed contact disposed at a top end part of a fixed terminal extending to a position closer to the inner part of the case than the second flange of the spool; and
a movable contact disposed at a position closer to the inner part of the case than the fixed contact, the movable contact being brought into contact with or separated from the fixed contact by an attraction force of the electromagnet and a restoring force of a spring for supporting the movable contact, whereby a conduction state between a movable terminal conductively coupled to the movable contact and the fixed terminal is switched over,
wherein the second flange has an end edge part facing the top end part of the fixed terminal, and a low strength part, which is low in rigidity and on which stress concentrates, disposed along a portion demarcating the end edge part of the second flange, and the fixed terminal is secured to the first flange.
In the specification, the term xe2x80x9cfixed contactxe2x80x9d or xe2x80x9cfixed terminalxe2x80x9d means a xe2x80x9cNO contactxe2x80x9d, which is separated from a movable contact in a normal state (when the coil is fed with no current) or a fixed terminal with the NO contact provided thereon.
The electromagnetic relay constructed according to the present invention may include an NC contact, which is in contact with a movable contact in a normal state (when the coil is fed with no current), as will be described later.
It should be understood that some of the novel and unique features of the invention will effectively be operable even in the structures including a fixed contact and a fixed terminal, which are associated with the NC contact. In the description to be given hereunder, the present invention is applied to a relay structure associated with the NO contact, for simplicity of explanation.
In the first electromagnetic relay constructed according to the invention, if the coil is thermally expanded, a transmission of such a force as to act on a second flange (located at the inner part of the case) of the spool to expand the second flange is blocked or impeded in the low strength part. Meanwhile, the fixed terminal (=fixed terminal for NO contact) is secured to the first flange (located at the opened side of the case) of the spool. Therefore, even if the coil is thermally expanded, the end edge part of the flange located at the inner part of the case, which faces the top end part (fixed contact) of the fixed terminal, and the fixed contact are not displaced to the inner side of the case (toward the movable contact) (or its displacement is considerably reduced or it is displaced to the opened side of the case). For this reason, such an unwanted situation that the coil is thermally expanded, the spool is deformed, and hence the fixed contact (NO contact) is pressed against the movable contact, never happens. Accordingly, even in an abnormal state of overcurrent feeding, there is no chance that that the fixed contact (NO contact) is held while being in contact with the movable contact (viz., the relay has a function of self-interrupting the overcurrent.). In other words, even when the coil is heated to excessive temperature, the fixed contact can be separated from the movable contact to the opened side of the case. Accordingly, a probability that fire accident occurs owing to the conduction retaining is completely eliminated.
In particular, when the low strength part is designed such that it is broken by stress and heat caused by an abnormal expansion of the coil, the transmission of the force acting to pressing the fixed contact against the movable contact (viz., the force for displacing it toward the inner part of the case) is completely blocked. The fixed contact is reliably held at a normal position at which it is supported by the fixed terminal secured to the flange located on the opened side of the case (normal position=position sufficiently spaced apart from the movable contact when no current is fed to the coil). Accordingly, fire accident can be prevented with higher reliability.
The flange of the case opened side is used lubricant also as a base for the assembling of the relay. Accordingly, it is designed to be thick and having a high rigidity when comparing with the flange of the inner part of the case. Accordingly, where the fixed terminal is secured to the flange of the case opened side, the top end part (i.e., the fixed contact) of the fixed terminal is hard to displace toward the movable contact. The fixed contact is reliably held at a position separated from the movable contact while not affected by the deformation of the flange of the case inner part since the low strength part is present.
In the electromagnetic relay, the low strength part may consist of a thinned part. The low strength part may also consist of a plurality of holes (through hole or non-through hole) formed in the second flange. The thinned part is formed by grooving a surface the second flange at the inner side of the case.
The first electromagnetic relay contributes to solve the problem of the deformation of the spool by the pressure having the coil axial direction and the configuration recovery of the deformed spool which subsequently occurs. The reason for this follows. As seen also from FIG. 6A, when the spool is deformed to be expanded by the pressure having the coil axial direction, the end edge part of the flange facing the top end part of the fixed terminal (i.e., the part which is secured to the fixed contact) is greatly bent since the low strength part (groove or the like) is present. With the bending, a force applied to the top end part of the fixed terminal is greatly lessened. As a result, there is no or little chance that the spool is deformed by the coil axial directional pressure, and hence the fixed contact is pressed against the movable contact. Thence, the contact pressure reduction arising from the subsequent configuration recovery of the deformed spool is removed or lessened.
The electromagnetic relay of the embodiment is capable of suppressing the vibration and noise generated when the contact is closed (produces silencing effects). The reason for this is that the vibration caused when the movable contact hits the fixed contact is flexibly absorbed by the edge end part of the flange at the case inner part, which is disposed facing the top end part of the fixed terminal. More specifically, the edge end part is parted from the remaining portion by the low strength part. Accordingly, it is easy to be bent. The vibration is absorbed by its flexible deformation. As a result, the noise caused by the vibration is reduced.
Additionally, it is noted that the low strength partxe2x96xa1takes the form of the groove. This groove serves also as a barrier to prevent insulation deterioration by carbon particles generated when the contact is opened and closed.
In a preferred embodiment, the fixed terminal is secured to the first flange in a manner that a protruded part extending from the fixed terminal is press fit into a hole of the flange located at the case opened side of the spool, and a part near the fixed contact of the fixed terminal is brought into engagement with an engaging part of the flange located at the inner part of the case.
In the structure thus constructed, the fixed terminals are stably supported at both the sides thereof, and a sufficient positioning accuracy is secured without taking such a measure that the planting dimension is increased by increasing the thickness of the flange of the spool. Further, at a part near the contact (flange located at the inner part of the case), the fixed terminals are supported by merely engaging, not press-fitting. A chance that cutting dust produced by the press fitting enters the gap between the contacts, and hence contact fault occurs, is remarkably lessened.
In another preferred embodiment, the fixed terminal has the mounting structure as described above, the whole electromagnetic relay is sealed by applying thermosetting sealing material to the opened side of the case, the holes to which the protruded parts are press fit are formed as through holes opened to the case opened side, and the gaps between the through holes and the protruded parts press fit therein are filled with the sealing material.
With such an arrangement, the fixed terminals are secured to the flange located at the case opened side by press-fitting. Bonding action of the sealing material (effective even at high temperature) also contributes to the securing of the fixed terminal to the flange. Accordingly, in the thermal expansion of the coil, the fixed contact (NO contact)(i.e., the top end part of the fixed terminal) is reliably held at a normal position at which it is supported by securing it to the flange located on the opened side of the case (normal position=position sufficiently spaced apart from the movable contact when current is not fed to the coil).
In an additional preferred embodiment of the invention, the fixed terminal has the mounting structure as mentioned above, the engaging part prevents the fixed terminal from moving only in the lateral direction orthogonal to the coil axial direction, and the fixed terminal is movable at least in the coil axial direction at the engaging part.
With such a mechanical arrangement, although the fixed terminals are stably supported as a whole by the respective flanges, there is no chance that the top end part of the fixed terminal (i.e., the fixed contact) is displaced in such a direction that it is pressed against the movable contact, as the result of the deformation of the flange of the spool. Accordingly, occurrence of the conduction retaining, which will cause the fire accident as referred to above, is highly reliably avoided. Additionally, the silencing effect mentioned above is ensured. In this case, an impact produced when the movable contact hits the fixed contact is reliably transmitted to the flange (edge end part) located at the inner part of the case, through the bending (displacement) of the top end part of the fixed terminal with the fixed contact provided thereon. And the edge end part is bent to absorb the impact.
In yet another preferred embodiment, a gap is formed between the top end part (fixed contact) of the fixed terminal and the end edge part of the flange located at the inner part of the case.
With such a mechanical arrangement, it is reliably avoided at the initial stage that the top end part of the fixed terminal (i.e., the fixed contact) is displaced in such a direction that it is pressed against the movable contact, as the result of the deformation of the flange located at the case inner part. The fire or the like is reliably prevented, and the silencing effect is further enhanced. In this case, the impact produced when the movable contact hits the fixed contact is first absorbed by the bending of the top end part of the fixed terminal, as shown in FIGS. 5A and 5B. In turn, the top end part of the fixed terminal comes in contact with the end edge part, and hence the end edge part is bent to further absorb the impact. Thus, the impact is smoothly absorbed in two steps.
According to another aspect of the invention, there is provided a second electromagnetic relay comprising:
a case having an opening at one end thereof and covering the whole electromagnetic relay;
a spool with a coil as an electromagnet wound therearound, the spool including a first flange disposed inside the case and at an opened side of the case, and a second flange disposed at an inner part of the case;
a movable iron member, on which attraction force of the electromagnet acts, disposed at a position closer to the inner part of the case than the spool;
a fixed contact disposed at a top end part of a fixed terminal extending to a position closer to the inner part of the case than the second flange of the spool; and
a movable contact, which moves in associated with the movable iron member, disposed at a position closer to the inner part of the case than the fixed contact, the movable contact being brought into contact with or separated from the fixed contact by an attraction force of the electromagnet and a restoring force of a spring for supporting the movable contact, whereby a conduction state between a movable contact terminal conductively coupled to the movable contact and the fixed terminal is switched over,
wherein the second flange has at least one protruded part disposed on an surface of the spool facing the inner part of the case, the protruded part coming in contact with the movable iron member to press the movable iron member to the inner side of the case when the spool is thermally expanded in a coil axial direction.
In the second electromagnetic relay, even if the spool is thermally expanded in the coil axial direction, the protruded parts come in contact with the movable iron member to press the movable iron member to the inner side of the case. Accordingly, even if the coil is thermally expanded, the thermally caused force to expand the flange of the spool, which is located at the inner part of the case, is transmitted to the movable iron member. As a result, the movable iron member and the movable contact coupled to the former move to the inner part of the case (move apart from the fixed contact) as the thermal expansion of the spool progresses. Therefore, even if the coil is thermally expanded and the fixed contact slightly displaces to the inner part of the case (toward the movable contact), there is less chance that the fixed contact is pressed against the movable contact and their conduction is retained.
Particularly, when a low strength part, which is low in rigidity and on which stress concentrates, is formed along a portion demarcating the end edge part of a flange located at the inner part of a case, which faces the top end part of a fixed terminal, and the fixed terminal is secured to a flange which is located at the opened side of the case, the synergy effect of the operation of the first electromagnetic relay (the fixed contact does not displace to the inner part of the case even if the coil is thermally expanded) and the operation of the second electromagnetic relay (the movable contact is forcibly displaced in such a direction that it moves apart from the fixed contact when the coil is thermally expanded) remarkably reduces a chance of retaining the contact-to-contact conduction. Accordingly, occurrence of the fire accident as referred to above is highly reliably avoided.
According to a third aspect of the invention, there is provided a third electromagnetic relay comprising:
a case having an opening at one end thereof and covering the whole electromagnetic relay;
a spool with a coil as an electromagnet wound therearound, the spool including a first flange disposed inside the case and at an opened side of the case, and a second flange disposed at an inner part of the case;
a fixed contact disposed at a top end part of a fixed terminal extending to a position closer to the inner part of the case than the second flange of the spool; and
a movable contact disposed at a position closer to the inner part of the case than the fixed contact, the movable contact being brought into contact with or separated from the fixed contact by an attraction force of the electromagnet and a restoring force of a spring for supporting the movable contact, whereby a conduction state between a movable terminal conductively coupled to the movable contact and the fixed terminal is switched over,
wherein the opening of the case is filled with thermosetting sealing material so that whole electromagnetic relay is sealed, and the fixed terminal is secured to the first flange.
In the third electromagnetic relay, when the flange of the spool outwardly deformed by the coil axial directional pressure displaces in the direction of lessening the spool deformation as the result of the aging after the coil is wound and the heat hardening process of the sealing material, it never happens that the top end part (i.e., the fixed contact) of the fixed terminal, together with the second flange (at the inner part of the case), displaces to the case opened side (apart in space from the movable contact), since the fixed terminal is secured to the first flange (located) on the case opened side. Rather than moving apart from the movable contact, it is pressed against the movable contact by the deformation lessening of the flange at the opened side of the casexe2x96xa1(the displacement to the inner part of the case) (viz., the pressure contact increases).
For this reason, the relay of the embodiment succeeds in solving the following problem: The contact pressure, which was adjusted to have an optimum value at the time of assembling the component parts within the case, varies to diminish, thereafter; As a result, it is impossible to secure a required contact pressure, and; The number of the resultant products, which fail to satisfy the required product specifications, is increased (viz., the product yielding decreases). Accordingly, the product yielding is remarkably increased. On the contrary, the contact pressure is increased, and the contact opening/closing performance and the opening/closing lifetime of the contacts are improved.
In the third electromagnetic relay, a specific mounting structure of the fixed terminal is such that a protruded part extending from the fixed terminal is press fit into a hole of the flange at the case opened side, and a part near the fixed contact of the fixed terminal is brought into engagement with an engaging part of the flange at the inner part of the case, as in the first electromagnetic relay. Such a mechanical arrangement accrues to the advantage of eliminating the contact pressure decreasing (or increasing the production yielding). Additionally, as already stated, the fixed terminals are stably supported, so that a sufficient positioning accuracy is secured. Further, a chance that cutting dust produced by the press fitting enters the gap between the contacts and contact fault occurs is remarkably lessened.
Where the mounting structure of fixed terminal is employed, it is preferable that the holes to which the protruded parts are press fit are formed as through holes, and the gaps between the through holes and the protruded parts press fit therein are filled with the sealing material. By so arranged, the fixed terminal is more firmly secured to the flange at the case opened side through the bonding action of the sealing material. The advantageous effects of the invention are more remarkably produced.
Where the mounting structure of fixed terminal is employed, it is preferable that the engaging part prevents the fixed terminal from moving only in the lateral direction orthogonal to the coil axial direction, and the fixed terminal is movable at least in the coil axial direction at the engaging part.
If so arranged, the top end part (or the fixed contact) of the fixed terminal is reliably held at a position at which it is positioned as the result of the support by the flange at the inner part of the case. Accordingly, the problem of the decreasing of the contact pressure is solved reliably (when the deformed flange resumes its original shape, the contact pressure is rather increased than decreased.)
Also, in the third electromagnetic relay, it is preferable that a gap is formed between the top end part of the fixed terminal and the end edge of the second flange.
With the provision of the gap, a deformation of the spool, which is caused when the coil is wound, is absorbed by the gap, and there is no or less chance that the fixed contact is pressed against the movable contact. Further, the problem of the contact pressure decrease caused by the deformation lessening, which follows it, is solved reliably.